In general, very diverse demands are made of such filter bags. For example, one goal in the design of such bags is to obtain a high level of filter effect, i.e., a high degree of dust collection. To that end, the filter pores must be sufficiently small. At the same time, however, the filter pores of the dust filter bag must not become clogged, either, so that a high suction or blowing output (e.g., of a vacuum cleaner) is maintained, and the need to replace the dust filter bag before a certain amount of filling has occurred, simply due to clogging, is avoided.
Furthermore, the dust filter bags must demonstrate sufficient mechanical strength, so that they do not tear or burst when they are set into place or when they are full. A corresponding level of strength is also necessary for the production of the bags, which entails a plurality of several folding steps.
Dust filter bags which are made of a porous non-woven material and a filter paper are known from European Patent No. 0 635 297 A1, and are processed to make double-ply dust filter bags. A melt-blown microfiber non-woven material can be used as the non-woven material, which covers the inside of the dust filter bag and reinforces the dust filter bag. Unfortunately, the degree of reinforcement provided by this bag is less than satisfactory.
Other dust filter bags are known from European Patent No.0 338 479 B1. The dust filter bag described there is composed of an outer layer of filter paper and a non-woven material. The non-woven material is structured as a microfiber non-woven material and faces the upstream side of the filter bag. In this connection, the microfibers of the non-woven material in the thermoplastic state can be directly deposited onto and connected with the filter paper. The microfiber non-woven material can be connected with a support element which is also made of non-woven material.
A disadvantage of the known dust filter bags is that in response to sucking in water or other liquid that may be drawn in with the air that is to be cleaned, the outer layer of filter paper becomes soft and loses its strength, creating the risk during vacuuming or removal of the dust filter bag of a tear in the bag or a soiling of the surroundings. The filter action with regard to microparticles is not very satisfactory.